( PF ~ ) ~ ~ ~ ~ ~ and [LRU'~(~-O)~RU~~L] - American Chemical Society

Jan 2, 2017 - and [LRU'~(~-O)~RU~~L](PF~)~.H~O. (L = 1,4,7-Trimethyl- 1,4,7-triazacyclononane). Peter Neubold,Ia Beatriz S. P. C. Della Vedova,la Karl...
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3355

Inorg. Chem. 1990, 29, 3355-3363

Contribution from Lehrstuhl fur Anorganische Chemie I, Ruhr-Universitat Bochum, D-4630Bochum, FRG, and Anorganisch-Chemisches Institut der Universitat Heidelberg, D-6900Heidelberg, FRG

Novel Cofacial Bioctahedral Complexes of Ruthenium: Syntheses and Properties of the Mixed-Valence Species [ L R u ~ . ~ ( ~ - X ) ~ R U L ]Br, ~ + I, OH). Crystal Structures (X~=. ~C1, ~ L[ L] R ( PUF' ~~( )~ ~- O~ )~~~R~U ~ ~ L ] ( P F (L~ = )~.H~O of [ L R U ~ ~ ~ ( ~ - O H ) ~ R U * ~and 1,4,7-Trimethyl-1,4,7-triazacyclononane) Peter Neubold,Ia Beatriz S . P. C. Della Vedova,la Karl Wieghardt,*sla Bernhard Nuber,lb and Johannes Weissib Received December 14, 1989

Reaction of RuCl,(dmso), with I ,4,7-trimethyl-1,4,7-triazacyclononane(L; C9HZ1N3) in ethanol affords red-brown LRu(dmso),CI2 (x = 1-2). which reacted with concentrated HX (X = CI, Br, I) in the presence of air to yield LRuCI,.H20, LRuBr,, and LRuI,. Treatment of these LRuX, species with CF,SO,H yielded gaseous HX and deep blue solutions from which the mixed-valence precipitated upon addition of ether. Blue [L2R~~5(p-X),](PF6)2 salts (X = CI, Br, I) were complexes [L,Ru,~~(~-X),](CF,SO,), was synthesized from an aqueous solution of [L,Ru,"'(p-O)!pisolated and characterized. Blue [L2R~22.5(p-OH)p](PF6)2-H20 CH3C02),](PF6),via reduction with zinc amalgam and exposure of the resulting yellow solution to air. Oxidation of this species with S20B2-at pH = 7 gave yellow [~,Ru,"'(p-OH),](PF,),, which reacted at pH 12 with O2to yield green [L2Ru2v(p-O),](1) and [LzR~2'V(p-o),](PF6)2.H20 (2) have been determined (PF6),.H20. The crystal structures of [L,Ru~~(~-OH),](PF~)~.H,O by X-ray analysis. Crystal data for 1: orthorhombic space group Pnma, a = 10.089 (2) A, b = 16.134 (3) A, c = 19.585 (4) A, V = 3188 ( I ) A,, Z = 4. Crystal data for 2: orthorhombic space group Pnma, a = 10.057 (5), 6 = 16.12 ( I ) A, c = 19.237 (9) A, V = 3 1 1 8.7 ( I O ) As,Z = 4. The (N,Ru(O),RuN,I core in both structures possesses idealized D,, symmetry. The Ru-Ru distances in 1 and 2 are 2.401 (2) and 2.363 (2) A, respectively. Electronic and ESR spectra have been recorded, and the magnetic properties of complexes have been investigated. The electrochemistryof mononuclear and binuclear species are reported. The = -0.46 V and E,,,, = + I ~ 1 V2 vs NHE, cyclic voltammogram of 2 in CH,N02 displays two reversible one-electron waves at which correspond to the couples E?,*

6'1/2

R U ~ " R Ue ' ~ Ru21VeRuIVRuV Scheme I

Introduction

Mixed-valence binuclear Ru'~Ru"' complexes of cofacial - 4biooctahedral geometry that contain three p-chloro or p-bromo Tf)L bridging ligands have received a great deal of attention during the past decades.2 Symmetrical and unsymmetrical binuclear t29 species have been synthesized and structurally ~ h a r a c t e r i z e d . ~ , ~ f+ ;R"* Their electronic structures have been investigated by various -H x s e spectroscopic techniques with respect to delocalized or trapped II I I m m IV valencies of the two ruthenium centers. Electrochemically, these RU RU R u ~ R u ~ Ru2 (RuX3RuJ2+complexes are often reversibly oxidized to yield the bond order: 0 0.5 1.0 2.0 { R U ' ~ I ( ~ - X ) ~ R U 'core ' I ] ~ +or reduced to produce the (Ru"(pX),RU'~J+m ~ i e t y .Furthermore, ~ Heath et aL4 have shown that preparative-scale electrogeneration of [ B~,RU'~~(~-B~)~RU'~B~~]~words, short M-M distances may be dictated by the steric reand even [ R U ~ I ~ ( C ( - B ~is) ~possible. B ~ ~ ] - Thus the binuclear coquirements for the three bridging groups rather than direct facial octahedral complexes of D3,, symnmetry are available in metal-metal bonding. This point has been analyzed by Cotton a wide range of formal oxidation states. and Ucko5 and others6 To complicate matters further, in contrast An intriguing and very interesting question of fundamental to the well-documented series CrzC193-,MO~C&,~-, and W2CIg3-, importance is the degree of direct metal-metal interaction where the former has no metal-metal bond and the latter two have (metal-metal bond order) as a function of the formal oxidation a strong M-M bond, in the present binuclear ruthenium complexes state of the respective ruthenium centers in these triply bridged the metal-metal bond is a priori weaker and the effect on the complexes. Obviously, an important parameter is the Ru-Ru structure is less pronounced and not readily detectable.* On the distance in such species. However, since we are dealing with triply basis of the very simple MO scheme for Ru2 complexes (Scheme bridged binuclear species, this distance is interdependent with other I) with D3h symmetry6,' the formal metal-metal bond order (BO) structural parameters of the {M(p-X),M) core, e.g. the M-X bond increases on going from Ru2'I (BO = 0), to Ru22,5(BO = 0.5), length and the M-X-M and the X-M-X bond angles. In other to Ru2'11(BO = I ) , to R U " ~ R U(BO ' ~ = 1.5), and to RuzlV (BO = 2) as electrons from antibonding orbitals a"2 and e" are stepwise removed. However, concomitant with the increasing Ru-Ru bond ( I ) (a) Ruhr-Universitlt Bochum. (b) Universitlt Heidelberg. order, the Ru-X distances decrease due to the reduced effective ( 2 ) (a) SchrMer, M.; Stephenson, T. A. In Comprehensive Coordination ionic radii of the oxidized ruthenium centers, and again, one is Chemistry; Wilkinson, G.,Gillard, R. D., McCleverty, J. A., Eds.; faced with the problem of which factor is more important in Pergamon Press: Oxford, England, 1987; Vol. 4, pp 277-478. (b) Seddon, K.;Seddon, E. A. The Chemistry of Ruthenium. In Topics in determining the Ru-Ru distance: the increasing Ru-Ru bond Inorganic and General Chemistry; Clark, R. J. H., Ed.; Elsevier: Oxorder or the steric requirements of the contracted, face-sharing, ford, England, 1984; Vol. 19. triply bridged {Ru(p-X),RuJ"+core. Only the combination of (3) (a) Heath, G. A.; Lindsay, A. J.; Stephenson, T. A,; Vattis, D. K. J . Organomet. Chem. 1982, 233, 353. (b) Contreras, R.; Elliot, G.G.;

+ +

~~

~

~

~~

~

~~~

Gould, R . 0.;Heath, G.A.; Lindsay, A . J.; Stephenson, T. A. J . Organomet. Chem. 1981, 215, C6. (c) Heath, G.A,; Hefter, G.; Robertson, D. R.; Sime, W. J.; Stephenson, T. A. J . Organomet. Chem. 1978. 152, C I . (d) Easton, T.; Heath, G. A.; Stephenson, T. A.; Bochmann, M. J . Chem. Soc., Chem. Commun. 1985, 154. (4) Coombe, V. T.;Heath. G.A.; Stephenson, T. A.; Vattis, D. K. J . Chem. Soc., Dalton Trans. 1983, 2307.

~~~

~

(5) Cotton, F. A.; Ucko, D. A. Inorg. C'him. Acta 1972, 6, 161. (6) Summerville, R. H.; Hoffmann, R. J. Am. Chem. Soc. 1979,101,3821. (7) Trogler, W. C. Inorg. Chem. 1980, 19, 697. (8) See, for instance, the discussion of the bonding in Ru"'~CI~(PBU where a Ru-Ru single bond is proposed (Ru-Ru = 3.176 (1) Cotton, F. A.; Matusz, M.;Torralba,C. Inorg. Chem. 1989, 28, 1516.

0020-l669/90/ 1329-3355$02.50/0 0 1990 American Chemical Society

A):

3356 inorganic Chemistry, Vol. 29, No. 18, 1990

Neubold et al.

structural data, magnetic properties, and electronic spectra of a series of similar complexes of the {Ru(p-X),Ru]"+ type is likely to produce a definitive answer. Species containing three chloro or bromo bridges have been fairly comprehensively characterized.2 Ru-CI and Ru-Br bonds a r e quite long (>2.2 A), and therefore, we felt that the above question concerning direct metal-metal bonding in these species is complicated by the steric constraints imposed by these large halide bridges on the ( R u ( ~ - X ) ~ Rcores. U ] Ru-OH or Ru-O bonds are significantly shorter and complexes containing three such bridges may be more informative. To our surprise, we found only

1

fw space group a, A

b, 8, c,

very few examples of such species in the literature. It appears that only complexes with a { R U ~ ~ ( ~ - O H ) , Rcore U ~ ' ~have + been structurally c h a r a ~ t e r i z e d . ~ - ~ No ' molecular species of the ~ R U ~ ~ ~ ( ~ - O H ) or , R( R U U~ ~. "~' ~( ~~- 'O H ) ~type ] ~ +have been described previously. We report here t h e synthesis, magnetic, and spectroscopic properties of [LzRuz(p-OH),]2+/3+and [LzRu21v(p-O)3]2+complexes all of which have been characterized by X-ray crystallography ( L = 1,4,7-trimethyl-l,4,7-triazacyclononane). Their electrochemistry is also reported. Some aspects of this work have been communicated previously.I2 In addition, the mixed-valence complexes [LzRu$.s(p-X)3]2+ ( X = CI, Br, I) have been synthesized from mononuclear precursors LRuX3.

Experimental Section The ligand 1,4,7-trimethyl-l,4,7-triazacyclononane(L)13 and the complex R ~ C I ~ ( d r n s were o ) ~ ~prepared ~ according to published procedures. LRuX, (X = CI, Br, I). To a mixture of RuCl,(dmso), (1.0 g, 2.1 inmol) in absolute ethanol (25 mL) was added 1,4,7-trimethyl-l,4,7triazacyclononane (0.80 g, 4.7 mmol) with stirring. The suspension was heated to 60 OC for 1 h until a clear deep red-brown solution was obtained, which was then heated under reflux for 2 h. The solvent was removed under reduced pressure by rotary evaporation. The red-orange residue (LRu(dmso),C12) was treated with concentrated HCI and heated under reflux for 30 min in the presence of air. An orange microcrystalline solid of LRuC13.H20 precipitated, which was collected by filtration, washed with H 2 0 , ethanol, and diethyl ether, and air-dried. Upon reduction of the volume of the reaction mixture further product may be obtained (yield: 0.49 g, 60%). Anal. Calcd for C9H2,N,0CI,Ru: C, 27.2; H, 5.8; N, 10.5. Found: C, 27.6; H. 5.8; N, 10.5. LRuBrl was prepared analogously by using concentrated HBr instead of HCI. Anal. Calcd for C9H2,N3Br3Ru:C, 21.1; H, 4.1; N, 8.2. Found: C, 20.9; H, 4.0; N, 8.1. LRuI, was prepared analogously by using concentrated HI. The solution was heated to only 80 OC for 1 h. Anal. Calcd for C9H2,NJ3Ru: C, 16.5; H, 3.2; N, 6.4. Found: C, 16.7: H, 3.0; N, 6.3. [ L R U ( N C C H ~ ) , ] ( P F ~To ) ~ a solution of LRuCI,.H20 (0.15 g, 0.38 mmol) in acetonitrile (IO mL) was added zinc powder (0.15 g), and the mixture was heated to reflux for 20 min. The yellow solution was filtered, and a solution of NaPF6 (0.4 g, 2.4 mmol) in CH$N (IO mL) was added. A yellow precipitate formed, which was filtered off and recrystallized from CH,CN (yield: 0.10 g, 38%). Anal. Calcd for C,SH,oN6P2F,2Ru:C, 26.3; H, 4.4; N, 12.3. Found: C, 26.0; H, 4.4; N, 12.1. [LRu~,~(~-X),RU~.'L](PF~)~ (X = CI, Br, I). To solid LRuX, (0.6 mmol), where X represents CI-, Br-, or I-, was added trifluormethanesulfonic acid (20 mmol. 3.0 g) with cooling. Gaseous HX was pumped (a) Arthur, T.; Robertson, D. R.; Tocher, D. A,; Stephenson, T. A. J . Oraanomef. Cfiem. 1981. 208. 389. (bl Gould. R. 0.: Jones. C. L.: Stephenson, T. A.; Tocher, D. A. J . Organomef. Cfiem. 1984,264,365. (c) Robertson, D. R.; Stephenson, T. A. J . Organomef. Cfiem. 1976, 116. C29. Kim, T. D.;McNeese. T. J.; Rheingold, A. L. Inorg. Chem. 1988, 27, 2554. 4shworth. T. V.: Nolte. M . J.; Singleton, E. J . Chem. Soc.. Chem. Commun. 1977, 936. Neubold, P.; Della Vedova, B. S. P. C.; Wieghardt, K.; Nuber, B.; Weiss, J. Angew. Cfiem. 1989, 101, 7 8 0 Angew. Cfiem.,Int. Ed. Engl. 19119 28. ..-., -. , 163 -Wieghardt, K.: Chaudhuri, P.; Nuber, B.; Weiss, J. Inorg. Chem. 1982, 21, 3086. Evans, I . P.;Spencer, A.; Wilkinson, G. J . Cfiem.Soc., Dalfon Trans. 1973. 204

A

v,A3

cm-l T, "C R Rw p,

2 897.7 Pnma (No. 62) Pnma (No. 62) 10.089 (2) 10.057 (5) 16.134 (3) 16.12 ( I ) 19.585 (4) 19.237 (9) 3118.7 (IO) 3188 (1) 4 4 0.71073 (Mo Ka; graphite) 1.88 1.91 11.32 11.57 22 22 0.067 0.054 0.056 0.049

900.7

off. The reaction mixture was slowly allowed to warm up to room temperature with stirring. After 1 h, the reaction mixture was again cooled to 0 OC, and dry diethylether was carefully added with efficient cooling. The product [LRu(~-X),RUL](CF~SO,)~ precipitated. After rapid filtration, the crude material was dissolved in water (5 mL). Solid NaPF6 (0.75 g; 4.4 mmol) was added to this solution, which initiated the precipitation of the desired [L2R~2(p-X)3](PF6)2 salts, which were collected by filtration, washed with cold water, and dried over P20s in vacuo (yield: ;.45%). Anal. Calcd for C18H42C13F12N6P2R~2: C, 23.0; H, 4.4; N, 8.9; CI, 11.3. Found: C, 22.6; H, 4.4; N, 8.5; CI, 11.3. Anal. Calcd for C18H42Br3F12N6P2R~2: C, 20.1; H, 3.9; N, 7.8. Found: C, 19.9; H, 3.7; N, 7.7. Anal. Calcd for C18H42F12N613P2R~2: C, 17.8; H, 3.5; N, 6.9. Found: C, 18.2; H, 3.5; N, 7.0. [LRu~.~(~-OH)~RU~~~L](PF~)~.H~O. A 0.05 M H2S04solution was in added to a mixture of [L2Ru211'(p-O)(p-CH3C02)~](PF6)2.0.5H~01' water (1 5 mL) and 25 g of zinc amalgam (3%) under an argon atmosphere until the pH of the solution was 2. The solution was stirred for 2 h at 40 "C. To this clear yellow solution were added NaOH (pH = 12) and NaPF6 (0.30 g; 1.8 mmol). The solution was then stirred in the presence of air at 40 OC until the color changed from yellow to deep blue. Slowly the precipitation of a blue microcrystalline product started. The mixture was stirred for another hour under an argon atmosphere and stored at 0 OC for 6 h. The blue precipitate was collected by filtration, washed with a small amount of ice-cold H 2 0 and dried in vacuo over P205. Recrystallization from a minimum amount of aqueous NaOH at suitable for an X-ray structure analysis (pH IO) p r o d u d single - crystals . (iield: 0.08 g, 35%). Anal. Calcd for CI8H4,Fl2N6O4P2Ru2:C, 23.9; H, 5.2; N, 9.3. Found: C. 24.1; H. 5.1; N, 9.4. 2 [L2Ru2"'(p-oH)3](PF6)3. To a solution of [ L 2 R ~ 2'(p-OH),](PF6)2+i20(0.10 g, 0.10 mmol) in water (15 mL) was added a solution of Na2S208(0.04 g, 0.16 mmol) in H 2 0 (3 mL) at 35 OC. The color changed from deep blue to yellow within a few minutes. After the solution was heated at 90 OC for 2-3 min followed by the addition of NaPF6 (0.25 g, 1.5 mmol), the reaction mixture was allowed to stand at 0 OC for 12 h. Yellow crystals precipitated, which were collected by filtration, washed with ethanol and ether, and air-dried (yield: 0.1 1 g, 95%). Anal. Calcd for C18H4SN603P3F18R~2: C, 21.0; H, 4.2; N, 8.2. Found: C, 20.8; H, 4.3; N, 7.9. [L2RU2'V(p-O),](PF6)2.H20. [L~Ru,"'(~-OH),](PF,), (0.10 g, 0.1 mmol) was dissolved in water (10 mL), and solid NaOH (0.02 g) was added with stirring. The solution was heated to 80 OC for IO min during which time the color changed from yellow to deep green. NaPF, (0.05 g, 0.3 mmol) dissolved in H 2 0 (1 mL) was added to the hot solution. Dark green crystals precipitated within 12 h in the refrigerator at 0 OC. These were collected by filtration, washed with ethanol and ether, and air-dried (yield: 0.05 g, 60%). Anal. Calcd for C18H44N604P2F12R~2: C, 23.5; H, 5.2; N, 9.0. Found: C, 23.8; H, 5.0; N, 9.1. X-ray Crystallograpby. Intensities and lattice parameters of a needle-shaped, black crystal of [L2Ru2(p-OH),](PF6)2.H20 ( I ) and a deep green, needle-shaped crystal of [L2RU2(p-o),](PF6)2.H20 (2) were measured on an AED I1 (Siemens) and a Syntex R3 diffractometer, respectively, at ambient temperature. Crystal parameters and details of the data collection and refinement are given in Table I (for full details ( 1 5)

Neubold, P.; Wieghardt, K.; Nuber, B.; Weiss, J. Inorg. Cfiem. 1989, 28, 459.

Inorganic Chemistry, Vol. 29, No. 18, 1990 3357

Bioctahedral Complexes of Ruthenium Table 11. Atom Coordinates (X104) and Temperature Factors

IO3) for [L2R~2(p-OH)3](PF6)2*H20 atom X Y z 569 ( 1 ) 2500 370 (1) Ru I 2500 9340 ( i j Ru2 9280 i i j 2500 -575 (5) 01 1200 (9) 02 -701 (8) 1657 (4) 53 (3) 2500 1448 (8) -100 (18) NI 3396 (7) 747 (5) N2 2034 (1 0) 2500 1513 (IO) CI -1551 (19) 3298 (14) 1722 (9) c2 464 (20) 3686 (9) 1421 (8) 1630 (18) c3 2914 (8) 839 (9) c4 3286 ( 1 2) 2193 (14) 4104 (8) 279 (6) c5 2500 -787 (7) -2858 ( 1 1) N3 -1502 (4) -817 (IO) 1620 (5) N4 2500 -121 (IO) -3519 (18) C6 3252 (9) -1202 (9) c7 -3191 (13) 1347 (11) -1544 (10) C8 -2272 ( 1 3) 2087 (6) -2138 (5) -427 (19) c9 931 (7) -1401 (7) 121 (14) CIO 4743 (2) 3499 (2) PI 1097 (4) 4683 (7) 3849 (6) 2433 (10) FI 1 F12 895 ( I 3) 3819 (5) 3408 (6) 1294 (13) F13 5698 (7) 3579 (9) 4711 (9) 2841 (5) 1859 (15) F14 3156 (7) -258 (IO) 4849 (9) F15 4681 (11) 4160 (6) F16 434 (15) 7500 3671 (9) 1604 (17) Walb

(A2 X

Table 111. Atom Coordinates (XIO') and Temperature Factors X

Lp

28 (1) 25 i i j 30 (4) 43 (3) 71 (8) 50 (4) 67 (IO) 218 (15) 94 (8) 118 (9) 64 (6) 48 (6) 43 (4) 90 (12) 93 (8) 132 (IO) 100 (7) 63 (6) 52 (1) 149 (6) 162 (6) 226 (9) 245 (10) 223 (8) 304 (11) 143 (IO)

lo') for [L2Ru2(p-o),](PF6)2.Hzo atom X Y Ru 1 715 ( I ) 2500 2500 -572 ( I ) Ru2 -1202 (9) 2500 01 3327 (4) 02 664 (8) 2500 NI 2840 (12) 826 (IO) 3366 (6) N2 -3230 (14) 2091 (8) CI c2 923 (8) -2170 (14) 1323 (8) -1532 (18) c3 3470 (18) 2500 c4 c5 -I09 (13) 4064 (8) 70 (17) 2500 N3 -1987 (IO) 1624 (7) N4 427 (19) C6 2906 (7) c7 1526 (19) 2500 C8 3152 (15) 1759 (IO) 2180 (16) 3677 (1 1) c9 1704 (15) CIO -462 (20) 5252 (2) 1095 (4) PI 6175 (6) 908 (1 2) FI 1 4307 (7) 1289 (13) FI 2 2434 (IO) 5313 (7) FI 3 5287 (11) F14 401 (15) -249 (1 0) FI 5 5139 (9) 1796 (15) F16 5243 (IO) Wal* 1570 (18j 2500 .

I

(A2

z

Lp

5669.9 (6) 4631.7 (6) 5562 (4) 4944 (4) 5790 (7) 6498 (5) 4174 (IO) 4708 (7) 3586 (7) 5129 (IO) 6388 (6) 3570 (8) 4248 (5) 7109 (6) 3528 (IO) 6178 (9) 6526 (IO) 3295 (IO) 8499 (2) 8409 (6) 8557 (8) 8841 (6) 9148 (5) 8164 (7) 7838 (5) 8655 (IO)

29.6 (4) 32.8 (4) 32 (4) 49 (2) 43 (5) 49 (4) 123 (9) 72 (6) 104 (8) 95 (11) 59 ( 5 ) 69 (7) 53 (4) 104 (8) 74 (IO) 102 (8) 125 (IO) 209 (14) 57 (1) 154 (6) 205 (8) 153 (6) 277 (10) 225 (8) 243 (9) 181 (12)

Equivalent isotropic U defined as one-third of the trace of the orthogonalized U,j tensor. bPosition of the oxygen atom of the water molecule of crystallization.

"Equivalent isotropic U defined as one-third of the trace of the orthogonalized U, tensor. bPosition of the oxygen atom of the water molecule of crystallization.

see Table SI in the Supplementary Material). Empirical absorption corrections (+ scans of seven reflections with 9 < 28 < 51') were carried out in each case.I6 Both structures were solved by conventional Patterson and difference Fourier methods. The function minimized during fullmatrix least-squares refinements was ~ w ( l F , , l -IF,I)* where w = l/$(I). Neutral-atom scattering factors and anomalous dispersion corrections for non-hydrogen atoms were taken from ref 17. The positions of the hydrogen atoms of the meth lene groups were placed at calculated positions with d(C-H) = 0.96 and group isotropic thermal parameters while the methyl groups were treated as rigid bodies, each with three rotational variables. All non-hydrogen atoms were refined with anisotropic thermal parameters. Final positional parameters for 1 and 2 are given in Tables 11 and 111, respectively. Instrumentation. Magnetic susceptibilities of powdered samples were measured in the temperature range 90-298 K by using the Faraday method. The susceptibility of [L2Ru2(p-O)3](PF6)2~H20 was measured in the range 2.3-299 K on a Foner magnetometer. Diamagnetic corrections were applied with use of Pascal's constants. X-band ESR-spectra were recorded on solid samples or frozen dmso solutions cf = 9.4217 GHz, P = 20 qW, modulation amplitude = 1 mT) on a Bruker ER 200 ESR spectrometer. Infrared spectra were recorded on a Perkin-Elmer 1720X FTlR spectrometer (KBr or Csl disks). The UV-vis/near-IR spectra were recorded on a Perkin-Elmer Lambda 9 spectrophotometer. The 400-MHz 'H NMR spectra were recorded on a Bruker AM 400 FT spectrometer. Electrochemistry. The apparatus used for electrochemical measurements has been described previously.I* Cyclic voltammograms (CV) were usually recorded in acetonitrile (0.1 M tetra-n-butylammonium hexafluorophosphate, [TBAIPF,, as supporting electrolyte) under an argon atmosphere. At the beginning of each experiment a CV of the solution containing only the supporting electrolyte was recorded. To this solution were then added solid samples (=IO-' M). A nearly equimolar amount of ferrocene was added as an internal standard. The working electrode was a platinum-button, glassy-carbon, or gold electrode; the reference electrode was an Ag/AgCl (saturated LiCl in C,H,OH) electrode and a Pt-wire auxiliary electrode was used. The redox potentials were measured against the internal standard ferrocenium/ferrocene

Scheme II

x

(1 6) Computations were carried out on an ECLIPSE computer by using the

program package SHELXTL (Sheldrick, G.M. Universitat Gottingen; Revision 5.1). ( 1 7) International Tablesjor X-ray Crystallography; Kynoch: Birmingham, England, 1974; Vol. IV, pp 99, 149. (18) Backes-Dahmann, G.;Herrmann, W.; Wieghardt, K.; Weiss, J. Inorg. Chem. 1985, 24, 485.

green

CH3

(Fc+/Fc), for which a redox potential in CH'CN of 0.40 V vs the normal hydrogen electrode (NHE) was assumed.19 Criteria for the reversibility of electrode processes were those of Nicholson and Shain.20

Results and Discussion Syntheses. Scheme I1 summarizes t h e synthetic routes and complexes prepared in this work. T h e reaction of R~Cl,(dmso),,'~ where dmso represents dimethyl sulfoxide, and the cyclic triamine L in refluxing ethanol affords a red-brown solution. Upon removal of t h e solvent under reduced pressure, a red-orange solid was obtained, t h e composition of which varied somewhat depending on the reaction conditions. Elemental analyses showed that t h e RuCI ratio was constant a t 1:2 b u t t h e ratio dmso:Cl varied between 2:2 a n d 3:2. T h e material is formulated as [LRuCIz( 1 9 , (a) Kcepp, H. M.; Wendt, H.; Strehlow, H. Z . Elekrrochem. 1960,64, 483; (b) Gag& R. R.; Koval, C. A.; Lisensky, G.C. Inorg. Chem. 1980, 19, 2855. (20) Nicholson, R. S.; Shain, I. Anal. Chem. 1965, 37, 178; 1964, 36, 706.

3358 Inorganic Chemistry, Vol. 29, No. 18, 1990

Neubold et al.

Table IV. Electronic Spectra and Magnetic Moments of Complexes complex A,,, nm (c = L mol-' cm-')rr LRuCIPH,O 397 (2.3 X 10% 340 (shL . , 300 (1.3 X IO3) not measured not measured 1650 (300), 684 (6.15 X IO3), 441 (805), 330 (970). 290 (sh) 763 (4.1 X IO3), 474 (690), 340 (1.2 X IO3). 300 (sh) 742 (2.7 X 10)) 1540 (240), 648 (3.3 X IO3), 354 (925) 1634 (320), 1450 (sh), 1150 (200), 1050 (200), 314 (7.4 X IO3) 1010 (900), 964 (750), 612 (460), 391 (1.9 X IO3) 328 (265) a

magnetic moment, fiB 2.35 (293 K), 2.1 1 (293 K ) , 2.28 (293 K), 1.88 (293 K), 1.83 (293 K), 2.20 (293 K), 1.75 (100-293

1.94 (98 K) 1.96 (98 K ) 1.94 (103 K ) 1.90 (98 K) 1.70 (98 K ) 1.99 (98 K )

K)

diamagnetic see text diamagnetic

Measured in CH3CN solution; extinction coefficients are per monomer or dimer.

The magnetic moments of powdered samples of LRuX, com(dmso),](dmso), (x = 0-1). This solid proved to be a very useful plexes in the temperature range 98-298 K (Table IV) are typical starting material for compounds containing the LRu fragment. for low-spin octahedral ruthenium( 111) complexes. Due to large Thus heating mixtures of this complex and concentrated hydrohalic spin-orbit coupling at room temperature, these observed penvalues acids (HCI, HBr, HI) in the presence of air resulted in the forare larger than the spin-only value of 1.73 pB. The observed mation of LRuX, species in good yields. Orange LRuC13.H20, temperature dependence is in line with that for compounds such red LRuBr,, and brown LRul, were obtained in this fashion in as [ R u ( N H ~ ) ~23)and ~ + [ R U ( N H , ) ~ C I ] and analytically pure form. ~ + ~other ~ octahedral Rul" complexes.2 The ESR spectrum of a solid sample of In an attempt to replace the halide ligands in the LRuX, species LRuCI3.H20 at 10 K displays an axial g-value pattern. The spin by a better leaving group such as the CF3S03-ion, we treated Hamilonian for an isolated low-spin dS ruthenium(II1) center (S these compounds with trifluormethanesulfonic acid with effective = takes the form shown in eq 1 .24 Two resonances at g,= cooling of the reaction mixtures. In a very exothermic reaction, gaseous HX evolved, which was pumped off. The color of the H = g,,PHJz+ g,P(HJx + H $ y ) (1) solutions turned deep blue or black during this process. Addition of diethyl ether initiated the precipitation of deep blue micro1.29 and g, = 2.92 are observed where the latter is more intense crystalline solids of [ L R u ~ ~ ~ ( ~ - X ~ ) R U ~ ~ ~Thus L ] (diC F ~ S Othan ~ ) ~the, former.2s merization with concomitant reduction to mixed-valence species [ L R u " ( N C C H , ) ~ ] ( P F ~is)diamagnetic. ~ Its electronic specand oxidation of X- to X2 is observed. We have not been able trum shows a maximum at 328 nm with a relatively large molar to synthesize a mononuclear LRu"'(O,SCF,)~ complex via this absorption coefficient of 265 L mol-I cm-I. In the 400-MHz ' H route. Recrystallization of the above salts from water and addition NMR spectrum of this species in CD3CN, a complicated multiplet of NaPF, yield the pure salts [LRU~.~(C(-X)~RU~~~L](PF~)~ (x = is observed at 2.90 ppm (midpoint) (12 H), which is typical for CI, Br, I). methylene protons of the coordinated cyclic triamine and a singlet Reduction of LRuC13.H20 in acetonitrile with zinc affords a (9 H) for the three methyl groups of the cyclic amine at 2.85 ppm. yellow solution from which, upon addition of NaPF,, yellow The signal of the methyl protons of the coordinated acetonitrile crystals of [ L R u " ( N C C H , ) ~ ] ( P F ~precipitated. )~ ligands appear at 6 = 2.45. The integral of this signal does not Complexes containing three bridging hydroxo or oxo groups correspond to the expected nine protons since slow exchange of were prepared under anaerobic conditions from [L2Ru:"(pCH3CN ligands by deuterated solvent molecules occurs. This has O)(p-CH3C02)2](PF6)2'5 by reduction of an acidic aqueous soalso been observed in [Ru(CH,CN),]~+where the methyl proton lution (pH = 2) of this species with zinc amalgam. The color signal was observed at 6 = 2.59.26 of the violet solution changed to yellow. After removal of the Zn (b) Binuclear [ L R U ~ . ~ ( ~ - X ) , R U ~(X. ~= L Cl, ] ~ +Br, I) Complexes. amalgam, the pH was adjusted to 12 (NaOH) in the presence The data for the electronic spectra and magnetic properties for of air and solid NaPF, was added. The color of the solution the mixed-valence complexes [ L2Ru22,5(p-X)3] ( PF6)2are sumchanged to deep blue, and crystals of [L2Ru22.s(p-OH)3]- marized in Table IV. Electronic absorption spectra were recorded (PF,),.H20 precipitated. Oxidation of an aqueous solution (pH in acetonitrile at ambient temperature. Spectra of the tris(p= 7) of this complex with peroxodisulfate affords yellow crystals chloro) and the tris(p-bromo) complexes are dominated by an of the oxidized form [L2R~21"(p-OH)3](PF6)3. Aqueous solutions intense absorption in the visible region and a weak absorption in of this species at pH > 12 were found to be air-sensitive. Thus the near-infrared region (near-IR), which have been assigned to the yellow color changed at 80 "C within 10 min to green. Adu u* (al' a;) and 6* u* (e" ):a excitations according dition of NaPF6 initiated the precipitation of [L2Ru2'v(p-O)3]to Hush, Beattie, and Ellis2' (Scheme I). Dubicki et a1.28have (pF6) 2*H20. concluded from MCD spectra of such complexes that the visible Spectroscopic and Magnetic Properties. (a) Monomers. In absorption must also contain a number of other electronic states monomeric complexes LRuX,, the N3RuX3polyhedron possesses of which one major component is the 6 x (e' e') (2E") idealized C,,symmetry since the cyclic triamine enforces a facial transition. arrangement of the nitrogen and halogeno donor atoms, respecThe electronic spectrum of [L2R~2Z~s(p-OH)3] (PF6)2.H20is tively. In the infrared spectrum of LRuCI3.3H20 (CsI disk), two fully in accord with the above spectra (Figure 1). An intense Ru-N and two Ru-CI stretching frequencies have been observed at 475,440 cm-' and 321, 297 cm-I, respectively. Two bands at 258 and 230 cm-' may be assigned to N-Ru-N deformation (23) Figgis, B. W.; Lewis, J.; Mabbs, F. E.; Webb, G. A. J . Chem. SOC.A 1966, 422. modes. The Ru-CI frequencies are in good agreement with those (24) (a) Stanko, J. A.; Peresie, H. J.; Bernheim, R. A.; Wang, R.; Wang, reported for ~ U C - [ R U ( N H ~ ) at ~ C310 I ~ and ] ~ ~280 cm-l. P. S. Inorg. Chem. 1973, 12,634. (b) Bunker, C.; Drago, R. S.; HenThe electronic spectrum of LRuCI3.H20 displays three ligdrickson, D. N.; Richmann, R. M.; Kessell, S . L. J . Am. Chem. SOC. and-to-metal charge-transfer (CT) bands (Table IV). According 1978, 100, 3805. (25) Hathaway, B. J.; Billing, D. E. Coord. Chem. Reu. 1970, 5 , 143. to the established assignment of similar absorption maxima in (26) Rapaport, 1.; Helm, L.; Merbach, A.; Bernhard, P.; Ludi, A. Inorg. [ R u C I , ] ~ the - ~ ~maxima at 397, 340, and 300 nm are A tZgCT Chem. 1988, 27, 873. bands. The low solubilities of LRuBr, and LRu13 in CH,CN did (27) Hush, N. S.; Beattie, J. K.; Ellis, V . M. Inorg. Chem. 1984, 23, 3339. not allow the recording of their solution spectra. (28) (a) Dubicki, L.; Ferguson, J. Chem. Phys. Left. 1984, 109, 129. (b)

- -

- -

- -

~~

~~~

~~~

~

-

(21) Durig, J. R.; Omura, Y . ;Mercer, E. E. J . Mol. Strucf. 1975, 29, 53. (22) Jorgensen. C. K . Mol. Phys. 1959, 2, 309.

Dubicki, L.; Ferguson, J.; Krausz, E. R. J. Am. Chem. SOC.1985, 107, 179. (c) Dubicki, L.; Ferguson, J.; Lay, P. A,; Maeder, M.; Magnuson, R. H.; Taube, H. J . Am. Chem. SOC.1985,107,2167, (d) Dubicki, L.; Krausz, E. Inorg. Chem. 1985, 24, 4461.

Inorganic Chemistry, Vol. 29, No. 18, 1990 3359

Bioctahedral Complexes of Ruthenium

I

I

\

10.8

I B

V

350

300

Figure 2. X-band

LdO

V

,

ESR spectra of [L,RU,(~-OH),](PF~)~.H~~ at IO K:

(a) frozen dmso solution; (b) solid sample. LOO

600

800

1000 A [nml

1200

1hOO

Electronic spectra of (a) [LzRuz(r-OH),](PF6)z.Hz0 (-), (b) [LzRU~(P-OH),I(PF~), (--I$ and (C) [L~R~z(~-O,I(PF~)ZHZO in CH3CN solutions and at 20 "C. Concentrations: (a) 3.8 X IO-" M; (b) 1.95 X IO-" M; (c) 3.7 X IO-" M (I-cm cell). Absorption maxima in the near-IR region are listed in Table IV. Figure 1.

(a**)

X-Band ESR Spectral Data for [L~RU~(C(-X),](PF~)Z Complexes at IO K g values 2.13, 1.90" [L~Ru~C~I(PF~)Z

Table V.

[LZRU~B~~~(PF~)~ [LzRUz131(PF6)z [LzRU2(OH)31(PF6)z.HzO

2.12, 2.23, 2.23, 2.10, 2.02,

3.6

2.09, 1.906 2.03b 2.14, 1.95' 2.02, 1.9Y

1.946

6

3.L

3.2

Figure 3. 400-MHz 'H NMR spectrum of [LZRu2(OH),](PF6),in CD,CN. Signals of the methylene protons of the coordinated ligand are shown only.

spectra typical of a uniaxial species; the corresponding g values are very similar to those reported here. Other mixed-valence species exhibit similar g-value patterns.3b For a more detailed absorption in the visible region at 648 nm (t = 3.3 X lo3 L mol-I analysis of these ESR spectra, see ref 28d. cm - I ) and an unsymmetrical low-intensity band at 1470 nm (c = 240) are observed. The width at half-height vi z, of both bands The yellow complex [ LzRu211'(p-OH)3] (PF,), is diamagnetic is significantly smaller than the [2310v,,,]1~22dpredicted for a in contrast to all tris(ha1ogeno)-bridged complexes, which display class I1 complex according to the Robin and Day clas~ification.~~ residual paramagnetism. The only diamagnetic analogue is Furthermore, the peak position and width of the band in the Wilkinson's organometallic complex [ (Me,P)6Ruz"'(p-CH2)3], near-IR region are independent of the polarity and nature of the which contains a short Ru-Ru distance of 2.65 A.31The 400solvent.30 Spectra have been recorded in acetonitrile, diMHz 'H N M R spectrum of the tris(c(-hydroxo) species in methylformamide, acetone, water, nitromethane, ethanol, diCH3CN-d3displays four resonances: two complicated multiplets chloromethane, dimethyl sulfoxide, and methanol: A,, = 15 400 (Figure 3) centered at 6 = 3.59 and 3.28 are assigned to the methylene protons of the coordinated triamines; a singlet of the f 150 cm-'; uI12= 4300 f 100 cm-I ([2310~,]~/~ = 6000 cm-l). This is taken as clear evidence that the valences in [LzRuz(p-X)3]2+ six methyl groups at 6 = 2.36 and a singlet of the O H protons species (X = CI, Br, OH) are delocalized; these complexes display at 6 = 8.75 are observed. In the 100-MHz I3C N M R spectrum (CH3CN-d3) a singlet at 6 = 56.5 (CH, groups) and a singlet at typical class I11 behavior. It is noted that in unsymmetrical complexes containing the {Ruz(p-X),]+core the degree of met6 = 64.6(CHz groups) are observed. The NMR spectra are fully al-metal interaction has been shown to decrease as the molecular in accord with D j h symmetry of the (N6R~2(OH)3)3+ core in solution. asymmetry increases.38 Magnetic moments of powdered samples of [L2R~22.S(pThe electronic spectrum of [LzRuz111(OH)3]3+ exhibits an inX)3](PF6)2(X = CI,Br, I, OH) in the temperature range 90-298 tense absorption maximum at 314 nm (c = 7.4 X IO3 L mol-l cm-I) which may be assigned to a u u* transition (al' a;) (Scheme K (Table IV) are in the range 1.88-2.20pB, which indicates the presence of one unpaired electron.3a X-band ESR spectra of solid I) and a series of weak transitions in the near-IR region (Table samples and frozen dmso solutions at 10 K were recorded; the IV) of which one may be of the 6* u* type. At present, we cannot assign these weak transitions in more detail but it is noted results are summarized in Table V. Figure 2 shows the ESR that octahedral monomeric LRuX, complexes do not show these spectra of [LzR~~~5(~-OH)3](PF6)2~H20 (a) as a solid sample and (b) as a frozen dmso solution at 10 K. The former displays absorption maxima. Interestingly and as is to be expected, the visible band ( u u * ) is shifted to higher energy on going from a rhombic g value pattern, but the solution spectrum shows a signal of uniaxial symmetry in agreement with the D3hsymmetry of the the mixed-valence { R U ( O H ) ~ R Uspecies ) ~ + to its oxidized form (Ru'~~(OH)~RU"')~+. ( N , R U ( O H ) ~ R U N core. ~ J ~ + For [LzRuz2~5(c(-Cl,)] (PF& the reverse is observed: a rhombic signal in frozen dmso and an axial The electronic spectrum of [L,RU'~~(~(-O)~](PF~),.H~O is also signal in the solid state. The frozen dmso solution ESR spectrum shown in Figure 1. We do not assign these bands because for of [L2R~z2.5(p-Br),](PF6)z displays an axial signal. Due to the reasons developed below it is not clear if a R U ' ~ - R Ubond ' ~ exists lability of [L2R~2z.5(p-I),](PF6)z in dmso solution, only a polyor not. Figure 4 shows plots of the magnetic moment, p, and the molar crystalline sample was measured at 10 K. A rhombic signal is susceptibility, xM,of [ L2R~~V(c(-o)3](PF6)z.Hz0 vs. temperature. observed. ESR spectra of [(NH3)6Ruz(p-C1)3]2+and of The latter exhibits a sharp increase of xM at temperatures below [(NH3)6R~2(r-Br)3]2+ in frozen glycerol/dmso at 60 K show ESR

" Polycrystalline sample. Frozen dmso solution.

-

-

-

-

( 2 9 ) Robin, M . B.; Day, P. Adu. Inorg. Chem. Radiochem. 1967, IO, 247. (30) Creutz, C. frog. Inorg. Chem. 1983, 30, 1.

(31) Hursthouse, M. B.; Jones, R. A.; Malik, K.M. A,; Wilkinson, G.J . Am. Chem. SOC.1979, 101, 4128.

3360 Inorganic Chemistry, Vol. 29, No. 18, 1990

Neubold et al.

-.0

50

150

100

I

200

250

&c

300

10'

TIKI

Figure 4. Plots of (a) molar susceptibility and (b) magnetic moment vs absolute temperature of [ L2Ru2(~-o),](PF6)2.H20.

Table VI. Selected Bond Distances (A) and Angles (deg) for [LlR~l(p-OH)3](PF6)l~H20 (1) and (in Parentheses) for ILIRu*(P-O)II(PF,)I'H~~ (2) Rul-01 1.96 ( I ) (1.937 (9)) Rul-02 1.969 (7) (1.918 (7)) Rul-NI 2.22 (2) (2.15 ( I ) ) Rul-NZ 2.20 ( I ) (2.14 ( I ) ) Ru2-01 1.943 (9) (1.899 (6)) Ru2-02 1.950 (7) (1.919 (7)) Ru2-N3 2.17 ( I ) (2.14 ( I ) ) Ru2-N4 2.18 ( I ) (2.14 ( I ) ) RuI-RuZ 2.401 (2) (2.363 (2)) 01-Rul-02 02-Rul-NI 02'-Rul-N2 02-R~l-02' N2-Rul-NZ' 02'-Ru2-02 02-R~2-N3 02-Ru2-N4 N3-RuZ-N4 RuI-OI-RUZ

85.1 (3) (84.5 (3)) 95.8 (4) (96.3 (3)) 177.4 (3) (176.5 (3)) 87.4 (4) (88.1 (4)) 82.4 (5) (81.6 (5)) 88.4 (4) (88.0 (4)) 95.2 (4) (95.9 (4)) 176.0 (3) (177.1 (4)) 82.5 (4) (82.6 (4)) 76.0 ( 3 ) (76.1 (3))

01-Rul-NI OI-Rul-NZ Nl-Rul-NZ N2-R~l-02 01-Ru2-02' OI-RUZ-N~ 01-Ru2-N4 02'-Ru2-N4 N4-Ru2-N4' R~l-02-Ru2

178.8 (5) (178.9 (4)) 95.7 (3) (97.2 (3)) 83.4 (4) (82.0 (4)) 95.1 (3) (95.1 (3)) 85.9 (3) (85.5 (3)) 178.3 (5) (178.1 (5)) 96.3 (4) (95.9 (3)) 95.0 (3) (94.6 (4)) 81.4 (5) (82.8 (6)) 75.5 (3) (76.0 (3))

30 K, which indicates the presence of a paramagnetic impurity ([L2Ruz(p-O),]+?). In the temperature range 50-300 K the magnetic moment varies between 1.39 and 2.31 pBper binuclear unit (or 0.98 and 1.63 pB per Ru'" ion). At high temperatures, the magnetic moment per binuclear unit approaches the limit of ~ 2 . pB, 6 which is c l a e to the value of 2.83 pBexpected for a triplet state (S = 1). This value would be in agreement with the simple molecular orbital scheme for a Ru-Ru bond of bond order 2 ( U ~ A ~ A * On ~ ) . the other hand, a recent magnetochemical study by Hatfield, Meyer et al.32on the monomeric, octahedral oxoruthenium(1V) complex ris-[Ru'v(bpy)z(py)(0)](C104)z has shown that this d4 species has a nonmagnetic ground state with the first excited state lying 79 cm-' higher in energy in the solid state. Thus the magnetic moment was found to vary between 1.95 pB at 50 K and ~ 2 . pB 7 at 300 K per RuIVcenter. It is therefore conceivable that the observed temperature dependence of the present binuclear ruthenium(1V) complex is indicative of an antiferromagnetic exchange coupling between two independent face-sharing octahedral Ru(1V) centers. Attempts to model the magnetic behavior by using the simple Heisenberg, Dirac, and van Vleck spin-exchange model (H= -WS1.Sz,SI = S2= 1) have failed. A more sophisticated treatment involving different models is obviously called for. Interestingly, very similar magnetic properties have been reported for the high pressure phase of BaRuiV03 and , binuclear face-sharing entities (03Ru2Ba Sr R U ' ~ O where 0,%O:f6are linked to chains via corner har ring.^)-^^ For comparison, the magnetic moments per Ru'" center i n Ba, ,&I/~RU'"O~ are 0.6 pugat 50 K and 1.25 pB at 300 K.,, &tal Structures. [ ~ z ~ ~ z 2 ~ s ( p - ~ ~( 1) ) 3and ] ( [L2R~21V(~-0)3)(PF6)z~Hz0 (2) crystallize in the orthorhombic space group fnma, and the respective lattice parameters are very similar. The unit cell volume of 1 is slightly larger than that of (32) Dobson,J. C.; Helms, J. H.; Doppelt, P.; Sullivan, B. P.; Hatfield, W. E.; Meyer, T. J. Inorg. Chem. 1989, 28, 2200. (33) Longo, J. M.; Kafalas, J . A. Murer. Res. Bull. 1968, 2, 687. (34) Donohue, P. C.; Katz, L.; Ward, R. Inorg. Chem. 1966, 5, 335. (35) Calaghan, A.; Moeller, C. W.; Ward, R . Inorg. Chem. 1966, 5 , 1572.

Structures and atom-labelingschemes for the dications in (a) [L2Ru2(r-OH)31 (PF6),-H20 and (b) [L2Ru2(r-0)31(PF~)~*HzO.

Figure 5.

~

2 in agreement with the fact that the Ru-N and Ru-0 bond distances of the binuclear cation in 1 are slightly larger than those in 2. Parts a and b of Figure 5 show the structures of the dications in 1 and 2, respectively. Selected bond distances and angles are summarized in Table VI. The dications possess crystallographically imposed site symmetry m; atoms Rul, Ru2, 0 1 , N3 and N1 lie on this mirror plane, which bisects the binuclear cations in both structures. Since the site symmetry m is not compatible with the (XXX) or (666) I conformation of the five-membered Ru-N-C-C-N chelate rings of the capping tridentate amine ligands L, the thermal ellipsoids of the methylene carbon atoms are unrealistically large and physically meaningless. They reflect a disorder that we have not been able to model satisfactorily by a split-atom model. This behavior is frequently encountered in crystal structure determinations of complexes containing coordinated 1,4,7-triazacyclononane ligand^.'^ The structures of the dications in crystals of 1 and 2 consist in each case of two ruthenium ions bridged by either three 1hydroxo or three p-oxo ions. Pseudooctahedral coordination at each Ru is completed by a facially coordinated 1,4,7-trimethyl1,4,7-triazacycIononane ligand. Thus the cations are cofacial bioctahedral. The most intriguing facet of these two structures are the short Ru-Ru distances of 2.401 (2) A in 1 and 2.363 (2) A in 2. For comparison, pertinent distances and angles of a number of face-sharing bioctahedral complexes of Ru are summarized in Table VII. It appears to be a common feature of cofacial binuclear ruthenium complexes that a considerable shortening of the Ru-Ru distance occurs upon one-electron oxidation of the (Ru"(p~ X),Rul')+ 6 ) z ~ ~ 2 to ~ ( R U ~ ( ~ - X ) ,species. core ) ~ + This difference is about 0.6 A for the tris(p-chloro) and the tris(p-hydroxo) species. This is indicative of a direct Ru-Ru bonding interaction in the mixed-valence forms. In D3* symmetry the tZgorbitals of octahedral ruthenium centers form a u (a]') and two A (e') bonding molecular orbitals and a u* (ai') and two K * (e") orbitals (Scheme I).,-' In the case of Ru2II, 12 electrons occupy these six orbitals, and (36) Chaudhuri, P.; Wieghardt, K. Prog. Inorg. Chem. 1987, 35, 329

Bioctahedral Complexes of Ruthenium

Inorganic Chemistry, Vol. 29, No. 18, 1990 3361

Table VII. Comparison of Structural Data for Face-Sharing Bioctahedral Complexes Containing a M(p-X),M Core

M-X, A

complex

2.1 5-2.21 2.080 (3) 2.09 (1) 1.955 (IO) 2.06 2.107 2.494 (3)

2.48 2.49 2.393 2.53 (3)

2.456 1.918 1.822 1.972 1.93 ( I )

M-X-M, den 90 91.5 90.9 (4)

(X = OH, 0, CI, Br)

X-M-X, den 75

IO

75.3 (5)

75.7 75.0

86.7 88.0

78.0

83 78.0 76.9

87.8 87.7 86 70.2

68.5 80.7 76 78.1 83.3 (6)

ref 11

9b this work

this work

31 39 40

79

41

90.3 92.4 85

37 38

84.3

8 this work 42 13

80.7 (3)

43

86.5

the resulting formal bond order is zero. Upon oxidation to R u ~ ~ . This ~ is the shortest Ru"'-Ru~~'distance reported for a cofacial dimers one antibonding electron is removed and the Ru-Ru bond binuclear Rul" complex. In Cotton's complex [Ru~''C~~(PBU~),], order is formally 0.5 ( u ~ K ~ A * ~ ) . this distance is 3.176 (1) A.8 In Wilkinson's diamagnetic complex However, Cotton and Uckos have pointed out that in bridged RU2l"(p-CH,),(PMe,)6], a short Ru-Ru distance of 2.650 (1) metal dimers some of the structural variables are interdependent, has been interpreted as a Ru-Ru bond of order 1 Conseand appreciable metal-metal bonding in triply bridged cofacial quently, we propose a metal bond ( ~ ~ ? r ~ ? rfor * ~ [L2Ru2"'(p) complexes should enforce M-X-M angles smaller than 70.5' and OH)J3+, which is supported by its diamagnetism. In contrast, X-M-X angles greater than 90'. The classic example is the series (Ru~~'(~L-CI)~RU~''J'* and their tris(p-bromo) analogues show reof [M2CI,13- complexes (M = Cr, Mo, W).6 If these criteria are sidual paramagneti~m,~~ but their structures have not as yet been strictly applied for the present series (Table VII) only in the determined by X-ray crystallography ( R w R u distances of >2.8 [(NH3)6R~22~S(p-CI)3]2+ 37 complex and its tris(p-bromo) anaA are expected). Finally, in diamagnetic [( [9]aneN3)2Ru211'(pl o g ~ ise Ru-Ru ~ ~ bonding indicated, whereas in the tris(p-hydroxo) OH)2(p-CH3C02)]13~H20, a Ru-Ru single bond at 2.572 (3) 8, complex (1) the short Ru-Ru distance could be a consequence has been observed ( ~ ~ i r ~ 6 ~ 6 * % that * ~ in ) this instance is clearly of the geometric constraints imposed by three bridging hydroxo established by its structural features, Le. acute Ru-OH-Ru and ligands. Interestingly, a short F+Fe distance of 2.509 (6) A in obtuse HO-Ru-OH bond angles.45 the analogous mixed-valent [L2Fe2.52(p-OH)3](C104)2. In [L2R~2'V(p-O)3](PF6)2-H20 an extremely short Ru-Ru CH30H.2H20 underscores this pointu since the high-spin (hs) distance of 2.363 (2) A appears to be in agreement with a metiron(I1) and iron(II1) ions are ferromagnetically coupled ( p = al-metal bond formally of the bond order 2 ( $ ~ ~ ? r * ~ )This . may 9,5 pg per binuclear dication) and no Fe-Fe bond is formed. The also be in accord with its magnetism. The effective magnetic same argument is true for [(NH,),CO~~'(~-OH)~CO"'(NH~)~]~+ moment approaches at temperatures >300 K the spin-only value where the Co.-Co distance is 2.565 A43 and for [L2Cr,"'(pfor two unpaired electrons per binuclear unit (Scheme I). OH)2]1,.3H20'3 where a Cr-Cr distance of 2.642 (2) A has been However, the structural data alone do not provide conclusive observed. The latter three complexes do not have direct bonding evidence for metal-metal bonding as is readily seen from a commetal-metal interactions. Therefore, although the Ru.-Ru disparison with other tris(p-oxo)-bridged structures (Table VII). In tance decreases by 0.6 A upon oxidation from (Ru2"(p-0H),)+ [L2Mn21V(p-O)3]2+, a very short Mn-Mn distance of 2.296 (2) to ( R u ~ ~ . ~ ( ~ - O the H ) structural ~ ) ~ + , features alone do not conA and a very strong ^antiferromagnetic coupling between the two clusively support the view that a Ru-Ru bond is formed. However d' centers (H= -WSl*S2; SI= S2 = 3/2; J = -390 cm-I) has been the electronic and the magnetic properties of 1 in conjunction with The M U M angles in both structures are larger than the structural data support this view more rigorously. 70.5' (76' for Ru;' and 78.1 for Mn,") and the 0-M-O angles The question as to whether a Ru-Ru bond is formed also arises are both smaller than 90'. These angles are again quite similar for [L2Ru2"'(p-OH)3](CI04)3~H20 and even more so for to those in complexes with an (M(p-OH),MJ3+core (M = Co, [L2R~21V(p-o)3](PF6)2.H20. For the former, crystals of very low Cr) where no metal-metal bonding O C C U ~ S . ~It~ should *~~ also be X-ray quality were obtained and the structure has been solved kept in mind that the d orbitals of a ruthenium(1V) ion are more and refined to a conventional R factor of 0.086 in the trigonal contracted as compared to their reduced forms Ru"' and Ru". s ace group P31c (C3u4), with a = 9.897 (6) A and c = 21.17 (1) The average RuIV-Ob bond length in 2 is 1.918 A, which is The standard deviations of bond distances and angles are large, longer than the corresponding distance in K4[CISRu-O-RuCIS] but the structure determination clearly revealed the connectivity containing a linear [Ru-O-RuJ6+ unit.46 In p-hydroxy-bridged of atoms to be same for the trication as in the dication of 1. A complexes of Ru"', Ru-O,,,, bond lengths of 2.02 A have been fairly reliable Ru-Ru distance of 2.505 (3) 8, has been determined. observed; this distance is 1.97 A in the mixed-valence complex

A

R

1. Hughes, M. N.; OReardon, D.; Poole, R. K.; Hursthouse, M. B.; Thornton-Pett, M. Polyhedron 1987, 6, 171 I . Beattie, J. K.; Favero, P.: Hambley, T. W.; Hush, N. S. Inorg. Chem.

-. .

1988. 2000. . 27. -. . ~

Rhodes, L. F.; Sorato, C.; Venanzi, L. M.;Bachechi, F.; Inorg. Chem. 1988, 27, 604.

Raspin, K. A. J . Chem. Soc. A 1969, 461. Laing. M.; Pope, L. Acta Crystallogr., Sect. E : Struct. Crystallogr. Crysr. Chem. 1976, 832, 1547. Wieghardt, K.; Bossek, U.; Nuber, B.; Weiss, J.; Bonvoisin, J.; Corbella, M.; Vitols, S. E.; Girerd, J. J. J . Am. Chem. soc. 1988, 110. 7398. Thewalt, U. 2.Anorg. Allg. Chem. 1975, 412, 29. DrOeke. S.; Chaudhuri, P.; Pohl, K.; Wieghardt, K.; Ding, X. Q.; Bill, E.; Sawaryn, A.; Trautwein, A. X.; Winkler, H.; Gurman, S. J. J . Chem. Soc., Chem. Commun. 1989, 59.

In summary, on the basis of the structural data for

[L2Ru22~s(p-OH)3](PF,)2~H20, [L2R~2111(p-OH)3] (CIO4), and [ L , R U ~ ~ ( ~ -(PF6),-H20 O)~] alone an unambiguous assignment of metal-metal bonding is not possible-despite two short and a very short Ru-Ru distance. In conjunction with their electronic spectra and magnetic properties, it appears to be reasonably safe to invoke such Ru-Ru interactions at least for the former two complexes. The structural and magnetic properties of (45) Wieghardt, K.; Herrpann, W.; Koppen, M.; Jibril, I.; Huttner, G. Z. Naturforsch. 1984, 396, 1335. (46) Deloume, J. P.; Faure, R.; Thomas-David, G. Acta Crystallogr., Sect. E : Srruct. Crystallogr. Cryst. Chem. 1979, B35, 5 5 8 .

3362 Inorganic Chemistry, Vol. 29, No. 18, 1990 Table VIII. Electrochemical Data for the Complexes" comdex E , I,. V

Neubold et al.

n

E.. V ~~

LRuC~~~

-0.59e -0.46e

+1.18d +1.14d

LRuBrt

[LRu(NCCH3)31(PF&' [L2RU2C131(PF6)z6 [LzRU2Br,l(PF6)2' [ L2R~2131(PFd2' [L2Ru2(0H)3](PF,)2.H*Ob [L2RU2(p-O)j](PF,)2*H206

+1.3Id +1.01, -0.19d +0.93,-0.09d +0.90, +O.OSd -0.1 I d + I .12, -0.46d

-1.3ff

a Experimental conditions: 0.1 M tetrabutylammonium hexafluorophosphate ([TBAIPF,), Pt-button working electrode, 20 OC, [complex] M. The redox potentials were measured against the internal standard ferrocenium/ferrocene, for which a redox potential in CH3CN of + 0 . 4 0 V vs NHE was assumed; the potentials are referenced vs the NHE. 'CHJCN solution. 'Acetone solution. Reversible. e Irreversible.

-

[L2Ru21V(p-o),](PF6)2.H20 do not rule out a metal-metal bond but do not provide conclusive evidence for it either. Electrochemistry. (a) Monomeric Complexes. Cyclic voltammograms (CV) for monomeric LRuX, (X = CI, Br, I) have been recorded in acetonitrile solutions (0.1 M [TBA]PF6supporting electrolyte) at a Pt-button working electrode at ambient temperature and scan rates of 20-200 mV/s. The results are summarized in Table VIII. The chloro and bromo complexes show a reversible one-electron oxidation wave at quite positive potentials, which corresponds to the couple [LRuX3]+10. At negative potentials an irreversible reduction peak is observed for both complexes, which is assigned to the generation of [LRu"XJ species that probably undergo halide substitution reactions with the solvent. At scan rates of >150 mV/s this process [LRuiVX3]+-4, LRu"'X, +e-

+e-

-

[LRu"X3]dissociation products (2)

is quasireversible. Interestingly, the electrochemical oxidation of the monochloro and dichloroammineruthenium(II1) complexes [(NH3)sRuC1]2+and [ R u ( N H ~ ) ~ C Ihas ~ ] +not been observed, but their reversible reduction to r~thenium(I1)~' is a feasible process. The CV for [ L R u ( N C C H ~ ) ~ ] ( P Fin, ) CH,CN ~ solution at a Au working electrode shows a reversible one-electron wave at +1.3 1 V vs N H E (eq 3). A coulometric measurement at +1.8 V confirmed a one-electron transfer ( n = 0.94 f 0.1). [LRu(NCCH3)J3+ + e-*

[LRU(NCCH,),]~+

(3)

It is noted that oxidation of [ R U ( N C C H ~ ) , ] ~has + not been observed up to +2.5 V.26 This is a demonstration of the stabilization of the RuI1 oxidation state by six r-acceptor acetonitrile ligands, which is reduced by substitution of three of these one 1,4,7-trimethyl- 1,4,7-triazacyclononane,which is a pure a-donor. Clark and Forda have estimated that one CH3CN ligand stabilizes the I1 oxidation state of ruthenium by ~ 0 . V. 4 This is nicely verified here. The redox potential of the couple [Ru([9]aneN3)2]3+/2+([9]aneN, represents 1,4,7-triazacyclononane)is +0.37 V vs NHE.45*49From Ford's correlation, a redox potential of + I S V is calculated for [LRu(NCCHJ,]~+/~+, which is to be compared with the experimental value of +1.3 V. The small difference of 0.2 V between the observed and calculated value may be due to a differing electronic effect of the two cyclic triamine donor ligands in both complexes (three secondary amine vs three tertiary amine N-donor atoms). The same correlation predicts a redox potential of =+2.7 V vs NHE for the [Ru(NCCH,),]~+/~+ couple. (b) Binuclear Complexes. Figure 6 shows the CV of [L2R~22,5(p-Br)3](PF6)2 in acetone (0.1 M [TBAIPF,) at a platinum working electrode in the potential range -0.5 V to +1.5 ~~

~

(47) Elson, C. M.; Itzkovich, I. J.; Page, J. A. Can. J . Chem. 1970,48, 1639. (48) Clark, R. E.; Ford, P. C. Inorg. Chem. 1970, 9, 227. (49) Bernhard, P.; Sargeson. A . M . Inorg. Chem. 1988, 27, 2582

V

Figure 6. cyclic voltammogram for [L2R~2(pBr)3](PF6)2 in acetone (0.1 M [TBA] PF,) at scan rates of 20, 50, 100 and 200 mV s-' at a plati-

num-button electrode. V vs Ag/AgCI reference electrode. Two reversible one-electron transfer processes are observed, which correspond to the couples designated in eq 4. The CV's of [L2R~22~s(p-CI,)](PFa)2 in €',I2

El112

[L2Ru2"X3]3++ e- C [L2Ru"Ru111X,]2++ e- e [L2RU2"X31+ (4) X = CI, Br, 1 acetonitrile and [L2R~3S(p-I)3](PF6)2 in acetone solution are very similar. The redox potentials E t l l zand EZl12are given in Table VIII. The difference (Elll2 - E2112!decreases on going from the p-chloro- to the p-bromo to the p-iodo-bridged species. A measure of the stability of the mixed-valence complexes [L2R~zX3]2+ is the comproportionation constant K , as defined in eq 5. From [L2Ru2'1'X3]3++ [L2Ru2"X3]+* 2[L2Ru22,sX3]2+K ,

(5)

the respective redox potentials, and E2112, values for K , are calculated to be 4.4 X lozofor X = CI, 1.8 X 10'' for X = Br and 2.4 X loi4for X = I. Thus the stability of the mixed-valence form decreases in the order p-CI > p-Br > p-I. Similar redox behavior has been reported for a series of asymmetric complexes of the type [ ( A S B , ) ~ - ~ C ~ , R U ~ ( ~ ( - C ~ , ) ] ' (where B represents p-tolyl, p-chlorophenyl, and phenyl) and [ (PEt2Ph)6-yC1YRu2(p-C13)]z.3*~b Two reversible metal-centered one-electron-transfer processes were observed, and K , varies from 2 X lo9 to 2.6 X lo2*. The stability of the mixed-valence form increases with increasing asymmetry of the coordination spheres of the two Ru centers. Furthermore, substitution of the neutral ligands by halide ligands decreases the redox potential for the process Ru21JJ+ e- * RuJIRul", and consequently, [Ru2CI9]* may be oxidized to the R U ' ~ ' R U species ~ at electrochemically accessible

potential^.^ The CV for [L,RU~~~~(OH)~](PF,)~-H~O in acetonitrile at a platinum working electrode shows only one reversible one-electron-transfer process, E l 1 2= -0.1 1 V vs NHE. A second irreversible reduction peak is observed at -1.30 V. The former corresponds to the couple [L2Ru2(OH)J3+12+whereas at a very negative potential an irreversible reduction to Ru211occurs. Up to a potential of +2.2 V vs Ag/AgCI no further oxidation step has been detected. The RU"'RU'~oxidation level is not accessible under these conditions in complexes with three hydroxo bridges. A sample of [L2Ru2"'(0H),](PF6), displays an identical CV. It is interesting that the replacement of three halide bridges in [L2Ru2XJ2+complexes by three hydroxo groups shifts the redox potentials to more negative potentials by =1 V. This indicates that the mixed-valence [L2Ru22.s(p-OH),]2+complex is more readily oxidized to the [12Ru,"'(p-OH)j]3+ form, which is a very stable species as compared to its [L2Ru,"1(p-X)3]3+ analogues.

3363

Inorg. Chem. 1990, 29, 3363-3371

The CV recorded on such an oxidized solution was identical with the CV shown in Figure 7. This indicates that on the time scale of a coulometric measurement (=30 min) the oxidized species is stable. The two one-electron-transfer reactions are thus assigned as in eq 6. Baar and Ansonso have recently reported on the RulvRuv

+RU21v+

R~IIIR~IV

-e-

-e-

Ell/*

E21,1

(6)

electrochemical behavior of dimeric complexes of Ru~~'Ru'" and RuiVformed by oxidative dimerization of [Rdti(edta)OH2]-. The probably oxo-bridged RuzrVbinuclear complex is capable of oxidizing water. It is interesting that three p-oxo bridging groups stabilize the RuIVoxidation state to such an extent that the RuIVRuVlevel is readilv accessible.

FclFc'

This may be interpreted as evidence for the existence of comparatively stronger metal-metal bonding in the p-hydroxo-bridged species. Upon oxidation of the mixed-valence form, an electron is removed from an antibonding molecular orbital of predominantly metal-metal character. The CV for [L2R~~V(p-O)3](PF6)2 in acetonitrile is shown in Figure 7. In the potential range -0.7 to +1.7 V vs Ag/AgCl, two reversible one-electron waves are observed at E l l l 2 = + I .I 2 V and E 2 1 / 2= -0.46 V vs NHE. A coulometric measurement at 1.05 V vs Fc+/Fc in nitromethane at a glassy-carbon working electrode established that the former corresponds to a one-electron oxidation of the binuclear Ru21Vspecies to the RuIVRuVmixedvalence species ( n = 0.99 f 0.05). The dark green color of the solution containing the Ru:" complex changed to green-yellow during this oxidation, and the visible absorption spectrum of such an oxidized solution displays maxima at 416,648, and 1320 nm.

Acknowledgment. We thank the Fonds der Chemischen Industrie for financial support of this work and the Degussa (Hanau, FRG) for a generous loan of RuC13.xHz0. We are grateful to Professor P. Gutlich (Universitat Mainz) for measuring the susceptibility of [LzR~2(p-0)3] (PF6)2-Hz0and Professor A. X. Trautwein (Medizinische Universitat Lubeck) for measuring the ESR spectra. Supplementary Material Available: A list of crystallographic details of the crystal structure determinations (Table SI) and tables of anisotropic displacement factors, H atom coordinates, bond lengths, and bond angles for 1 and 2 (9 pages); listings of observed and calculated structure factors for 1 and 2 (14 pages). Ordering information is given on any current masthead page. (SO) Baar, R. B.; Anson, F. C. J. Electroanal. Chem. Interfacial Electrochem. 1985, 187, 265.

Contribution from the Departments of Chemistry, Washington University, St. Louis, Missouri 63 130, and Louisiana State University, Baton Rouge, Louisiana 70803- 1804

Conformational Studies and Reduction Chemistry of a Bimetallic Cobalt(1) Carbonyl Complex Based on a Binucleating Hexakis(tertiary phosphine) Ligand System Andre D'Avignon,Ia Fredric R. Askhamtla and George G. Stanley*Jb Received January 2, I990 The 300- and 500-MHz IH N M R spectra of the bimetallic complex C O ~ ( C O ) ~ ( ~ H T(eHTP P ) ~ + = (Et2PCH2CH2)2PCH2P(CH2CH2PEt2)2)show a number of solvent-dependent and, in the case of acetone, temperature-dependent shifts of the central methylene bridge and chelate ring proton resonances. The results of two-dimensional IH J-correlated experiments, with and without 3'P decoupling, are presented to assign both 'H-IH and IH-"P coupling constants in acetone-d, and CD2C12. Broad-band IIP decoupling causes a spectacular simplificationof the highly coupled ' H spectra, allowing clear resolution of all resonances. van der Waals energy calculations are presented for a model complex of C O ~ ( C O ) ~ ( ~ H Tthat P ) ~show + the presence of several low-energy conformers differing by rotations about the central methylene bridge. The chemical shift changes for the P-CH,-P proton resonances are proposed to be caused by differing amounts of carbonyl shielding from different rotational conformers in solution. The changes in the chelate ring proton resonances are proposed to be caused by trigonal-bipyramidal F! square-pyramidal coordination geometry changes about the cobalt centers, which result in chelate ring conformationalchanges. The reduction of Coz(CO).,(eHTP)2+with naphthalenide anion produces the Co-Co-bondeddimer Co2(C0)2(eHTP)in 4040% yields. This very reactive material has been spectroscopically characterized, and both one-dimensional IlP N M R and two-dimensional s'P-31PCOSY N M R spectra for the product mixture are presented and discussed.